0:14Skip to 0 minutes and 14 secondsIn the next three weeks, we'll be looking at some broad areas in which effective logical and critical thinking is important and which generate distinct, or specific, approaches to the questions they address. We'll start this week with science. So how does critical thinking work in science? Let's look at an example. We begin with an observation and a question. Here is a famous one.

0:40Skip to 0 minutes and 40 secondsScientists noticed that there were, one, fossilised dinosaur bones in rock strata up until the end of the Cretaceous period, but not after, 2, many other types of terrestrial and marine fossils not present after the end of the Cretaceous period, 3, high iridium levels in rock strata at the boundary between the Cretaceous and the Tertiary periods, the KT boundary. What happened, at the end of the Cretaceous period, to explain those observations? Let's develop some hypotheses, some possible explanations for those observations. A, a supernova, the explosion of a star, occurred 65 million years ago and caused a change to conditions on Earth, which rendered them unsuitable for various types of organisms that had previously thrived.

1:34Skip to 1 minute and 34 secondsB, an asteroid collided with years 65 million years ago and had roughly the same effect. A and B both explain the high levels of iridium. Supernovas throw off heavy elements like iridium. Asteroids contain higher levels of iridium than the Earth's crust does. How do we choose between them? What we need is some kind of test. But is there one? Well, actually there is. Hypothesis A, the supernova theory, predicts not only high levels of iridium, but also a massive amount of plutonium 244 in the relevant strata because supernovas throw off plutonium 244 as well as iridium. Hypothesis B, the asteroid theory, predicts there is no plutonium 244. And no the plutonium 244 was found in the relevant strata.

2:34Skip to 2 minutes and 34 secondsTherefore, the correct answer is B. The asteroid hypothesis beats the supernova hypothesis. But not so fast. We know there have been lots of asteroid strikes on the Earth which haven't resulted in mass extinctions, so why would this particular one have killed off the dinosaurs and their friends? That raises a new question. How could this particular asteroid strike cause a mass extinction? Here's a hypothesis. The impact of a massive asteroid might have thrown up a lot of dust, blotting out the sun, and causing dramatic climate change. And to back up the second asteroid hypothesis, we would expect to find a large crater somewhere. The Gulf of Mexico looks like a good candidate.

3:29Skip to 3 minutes and 29 secondsWe will also expect to find various substances at the KT boundary, the time period when the dinosaurs became extinct. Things like tsunami debris, glass from the melding of rock, particles from the impact site. So what I hope we've done here is to give an example of how the scientific method works. The scientific method consists of a number of steps. One, identify a problem or pose a question. 2, devise a hypothesis to explain the event or the observation or the phenomenon. 3, derive a test for the hypothesis. 4, perform the test. And 5, accept or reject the hypothesis. That looks about right, but you have to be careful about the last step with accepting or rejecting the hypothesis.

4:30Skip to 4 minutes and 30 secondsWhy is that Dr. Logical? Well, that's because logic tells us that tests can lead us to reject hypotheses, but it can't conclusively settle that they're true. That's the distinction between verification and falsification.

Science and the scientific method

In the next three weeks, we’ll be looking at some broad areas in which effective logical and critical thinking is important and which generate distinct, or specific, approaches to the questions they address. We’ll start with science. This week, we aim to help you to: